Because both vessels were on near-parallel converging courses and the speed of the NAVEGANTE was greater than that of the TERESAMARIA and the NAVEGANTE had come up on the TERESAMARIA from a direction of more than two points abaft the beam, an overtaking situation existed. The NAVEGANTE, being the overtaking vessel, was obliged to keep clear of the TERESAMARIA. The TERESAMARIA was the stand-on vessel and was obliged to maintain her course and speed unless it became clear that collision could not be avoided by the action of the giving-way vessel alone. As the close-quarters situation developed, neither vessel took avoiding action as the distance between them reduced to between 15 and 25m. Because both vessels were on automatic steering at this time, the ability of the vessels' operators to make a rapid alteration of course was lessened. To meet her obligation under the Colregs to keep clear of the TERESAMARIA, the NAVEGANTE could have reduced speed or altered course or both. Neither of these options was exercised. When it became clear to the TERESAMARIA that the NAVEGANTE was not taking the action required of her, the TERESAMARIA could also have taken similar action to avoid collision, but did not. The TERESAMARIA attempted to establish radio communication to determine the intentions of the NAVEGANTE but received no reply, however, no attempt was made to sound the appropriate whistle signal to warn the other vessel that her intentions were unclear. The operator of each vessel was acting as sole navigator and look-out and both reported that they had a good understanding of the International Regulations for Preventing Collisions at Sea (Colregs). As such, each should have been able to make a full appraisal of the developing situation. However neither operator took action to prevent the development of the close quarters situation. Immediately before the collision the vessels were so close together that the operator of the TERESAMARIA believed that he saw the operator of the NAVEGANTE making adjustments to the instrumentation (auto-pilot) on that vessel's console. The operator of the NAVEGANTE, however, maintained that his vessel's steering mode was unchanged until after the collision. This information would appear to indicate that the NAVEGANTE did not sheer towards and collide with the TERESAMARIA as a result of a loss of control due to a change made in the mode of steering. Given that no fault developed in the automatic steering, the most probable explanation for the sudden sheer taken by the NAVEGANTE is that the sheer was due to hydrodynamic interaction between the two vessels which were proceeding at speed on near parallel courses. Although the operator of the NAVEGANTE was the holder of a Fishing Masters Class IV certificate and had received some training in the two weeks preceding the collision, he did not make a timely determination that a close-quarters situation was developing. A further indication that his training may not have been sufficient was that he did not keep an efficient radio watch because he did not respond to the VHF calls made by the TERESAMARIA. Although he did not speak English or French, those on board the TERESAMARIA were, like him, Portuguese speakers and there should have been no difficulty in communicating in that language. Although the principles of good seamanship and the provisions of the Canada Shipping Act require that the master or the person in charge of each vessel involved in a collision render assistance to the other vessel and to stand-by her until it is ascertained that such assistance is no longer required, the operator and master of the NAVEGANTE did not do so. The NAVEGANTE departed the scene without establishing the extent of the other vessel's collision damage or if she required assistance. Although a report of the occurrence was made to the Ontario Provincial Police by the TERESA MARIA, neither vessel reported the occurrence directly to TSB or to Transport Canada.Analysis Because both vessels were on near-parallel converging courses and the speed of the NAVEGANTE was greater than that of the TERESAMARIA and the NAVEGANTE had come up on the TERESAMARIA from a direction of more than two points abaft the beam, an overtaking situation existed. The NAVEGANTE, being the overtaking vessel, was obliged to keep clear of the TERESAMARIA. The TERESAMARIA was the stand-on vessel and was obliged to maintain her course and speed unless it became clear that collision could not be avoided by the action of the giving-way vessel alone. As the close-quarters situation developed, neither vessel took avoiding action as the distance between them reduced to between 15 and 25m. Because both vessels were on automatic steering at this time, the ability of the vessels' operators to make a rapid alteration of course was lessened. To meet her obligation under the Colregs to keep clear of the TERESAMARIA, the NAVEGANTE could have reduced speed or altered course or both. Neither of these options was exercised. When it became clear to the TERESAMARIA that the NAVEGANTE was not taking the action required of her, the TERESAMARIA could also have taken similar action to avoid collision, but did not. The TERESAMARIA attempted to establish radio communication to determine the intentions of the NAVEGANTE but received no reply, however, no attempt was made to sound the appropriate whistle signal to warn the other vessel that her intentions were unclear. The operator of each vessel was acting as sole navigator and look-out and both reported that they had a good understanding of the International Regulations for Preventing Collisions at Sea (Colregs). As such, each should have been able to make a full appraisal of the developing situation. However neither operator took action to prevent the development of the close quarters situation. Immediately before the collision the vessels were so close together that the operator of the TERESAMARIA believed that he saw the operator of the NAVEGANTE making adjustments to the instrumentation (auto-pilot) on that vessel's console. The operator of the NAVEGANTE, however, maintained that his vessel's steering mode was unchanged until after the collision. This information would appear to indicate that the NAVEGANTE did not sheer towards and collide with the TERESAMARIA as a result of a loss of control due to a change made in the mode of steering. Given that no fault developed in the automatic steering, the most probable explanation for the sudden sheer taken by the NAVEGANTE is that the sheer was due to hydrodynamic interaction between the two vessels which were proceeding at speed on near parallel courses. Although the operator of the NAVEGANTE was the holder of a Fishing Masters Class IV certificate and had received some training in the two weeks preceding the collision, he did not make a timely determination that a close-quarters situation was developing. A further indication that his training may not have been sufficient was that he did not keep an efficient radio watch because he did not respond to the VHF calls made by the TERESAMARIA. Although he did not speak English or French, those on board the TERESAMARIA were, like him, Portuguese speakers and there should have been no difficulty in communicating in that language. Although the principles of good seamanship and the provisions of the Canada Shipping Act require that the master or the person in charge of each vessel involved in a collision render assistance to the other vessel and to stand-by her until it is ascertained that such assistance is no longer required, the operator and master of the NAVEGANTE did not do so. The NAVEGANTE departed the scene without establishing the extent of the other vessel's collision damage or if she required assistance. Although a report of the occurrence was made to the Ontario Provincial Police by the TERESA MARIA, neither vessel reported the occurrence directly to TSB or to Transport Canada. Did not change steering mode from automatic to manual, to reduce rudder response time, until after they had collided. The NAVEGANTE most likely sheered towards and collided with the MARIA TERESA as a result of the hydrodynamic interaction between the two vessels which were proceeding at full speed on near-parallel courses about 15 to 25 m apart. Did not report the collision to Transport Canada, the Canadian Coast Guard or to TSB. The MARIA TERESA, however, made a report to the OPP. Although both operators claimed a good understanding of the Colregs, neither implemented the appropriate course of action as specified in the Colregs Steering and Sailing Rules. Was overtaking and was obliged to keep clear of the TERESAMARIA. Did not determine that a risk of collision existed and neither reduced speed nor altered course to avoid the development of a close-quarters situation. Did not maintain an efficient VHF radio watch. Did not attempt to establish contact with the TERESAMARIA either by VHF radio or by sound signals. The operator did not speak English or French but could have communicated with the TERESAMARIA in Portuguese. The operator was new to the vessel and, for the first time, had been left in sole charge of the navigation by the master. The operator did not inform the master of the NAVEGANTE that a close-quarters situation was developing or ask for his assistance. After the collision, the master did not ascertain the extent of the other vessel's damage or if it required assistance before the NAVEGANTE continued on passage. Being the stand-on vessel, maintained her course and speed as she was required to do by the Colregs. The operator established that the NAVEGANTE was not giving way and attempted to communicate with her by VHF radiotelephone. When it became apparent that the development of a close-quarters situation could not be avoided, the operator of the TERESAMARIA did not, as he was required to do by the Colregs, take such action as would best aid to avoid collision. Did not attempt to warn the NAVEGANTE of the developing situation by the use of sound signals. Being the stand-on vessel, maintained her course and speed as she was required to do by the Colregs. The operator established that the NAVEGANTE was not giving way and attempted to communicate with her by VHF radiotelephone. When it became apparent that the development of a close-quarters situation could not be avoided, the operator of the TERESAMARIA did not, as he was required to do by the Colregs, take such action as would best aid to avoid collision. Did not attempt to warn the NAVEGANTE of the developing situation by the use of sound signals.Findings Did not change steering mode from automatic to manual, to reduce rudder response time, until after they had collided. The NAVEGANTE most likely sheered towards and collided with the MARIA TERESA as a result of the hydrodynamic interaction between the two vessels which were proceeding at full speed on near-parallel courses about 15 to 25 m apart. Did not report the collision to Transport Canada, the Canadian Coast Guard or to TSB. The MARIA TERESA, however, made a report to the OPP. Although both operators claimed a good understanding of the Colregs, neither implemented the appropriate course of action as specified in the Colregs Steering and Sailing Rules. Was overtaking and was obliged to keep clear of the TERESAMARIA. Did not determine that a risk of collision existed and neither reduced speed nor altered course to avoid the development of a close-quarters situation. Did not maintain an efficient VHF radio watch. Did not attempt to establish contact with the TERESAMARIA either by VHF radio or by sound signals. The operator did not speak English or French but could have communicated with the TERESAMARIA in Portuguese. The operator was new to the vessel and, for the first time, had been left in sole charge of the navigation by the master. The operator did not inform the master of the NAVEGANTE that a close-quarters situation was developing or ask for his assistance. After the collision, the master did not ascertain the extent of the other vessel's damage or if it required assistance before the NAVEGANTE continued on passage. Being the stand-on vessel, maintained her course and speed as she was required to do by the Colregs. The operator established that the NAVEGANTE was not giving way and attempted to communicate with her by VHF radiotelephone. When it became apparent that the development of a close-quarters situation could not be avoided, the operator of the TERESAMARIA did not, as he was required to do by the Colregs, take such action as would best aid to avoid collision. Did not attempt to warn the NAVEGANTE of the developing situation by the use of sound signals. Being the stand-on vessel, maintained her course and speed as she was required to do by the Colregs. The operator established that the NAVEGANTE was not giving way and attempted to communicate with her by VHF radiotelephone. When it became apparent that the development of a close-quarters situation could not be avoided, the operator of the TERESAMARIA did not, as he was required to do by the Colregs, take such action as would best aid to avoid collision. Did not attempt to warn the NAVEGANTE of the developing situation by the use of sound signals. The vessels collided because the hydrodynamic interaction between them caused the NAVEGANTE to sheer to starboard and collide with the TERESAMARIA when both vessels were proceeding on near-parallel courses, at speed and in close proximity to each other. Contributing factors to the occurrence were: the NAVEGANTE, being the overtaking and give way vessel, did not give way; the TERESAMARIA, when it became apparent that the development of a close-quarters situation could not be avoided, did not take action to avoid collision; a lack of inter-ship communication; and the operators' level of training and knowledge of the Rules of the Road.Causes and Contributing Factors The vessels collided because the hydrodynamic interaction between them caused the NAVEGANTE to sheer to starboard and collide with the TERESAMARIA when both vessels were proceeding on near-parallel courses, at speed and in close proximity to each other. Contributing factors to the occurrence were: the NAVEGANTE, being the overtaking and give way vessel, did not give way; the TERESAMARIA, when it became apparent that the development of a close-quarters situation could not be avoided, did not take action to avoid collision; a lack of inter-ship communication; and the operators' level of training and knowledge of the Rules of the Road.